Description

Tangent galvanometers measure the strength of an electric current. When a current passes through the coil, it produces a magnetic field that is directly proportional to the current. This moves the needle on the compass with the vector sum of the unknown current in the coil, and the earth’s magnetic field. Because the magnetic field of the earth is constant, the current can then be measured as the tangent of the angle of deflection on the needle. Instruments like these were used in physics classrooms to demonstrate electrical principles.